Apple and amazon and facebook are all vulnerable. I'm not sure about microsoft, they are working harder to be independent. Apple controls the installation of apps on their platform, you can't easily go around it. They arbitrarily prevent competition as in browsers. Many many companies get no benefit from being in the app store and don't want to pay apple 30% of their revenues (think disney, amazon, netflix). Apple doesn't have a way to unlock their phones and go around these limitations. If they did then you could argue they aren't blocking competition. Apple (and all these companies) all do some things I see as positives too.